1. Field of the Invention
The present invention relates to a silicon carbide semiconductor device, more particularly, a silicon carbide semiconductor device having a contact electrode in contact with a silicon carbide substrate.
2. Description of the Background Art
In recent years, silicon carbide substrates are now being used for manufacturing semiconductor devices. Silicon carbide has a bandgap larger than that of silicon. Therefore, a semiconductor device employing a silicon carbide substrate advantageously has a high breakdown voltage, low ON resistance, and less property deterioration in a high temperature environment.
As a method of forming an ohmic electrode for silicon carbide, metal material including Ni or Al is vapor-deposited on an impurity region doped at high concentration. Then, the metal material is subjected to rapid thermal treatment at the temperature of approximately 1000° C. to form a reaction layer. Thus, ohmic contact is established between the reaction layer and silicon carbide (refer to Hiroyuki Matsunami et al. “Semiconductor SiC Technology and Application (Second Version)”, Nikkan Kogyo Shimbunsha, Sep. 30, 2011, pp. 298-309)
Although Ni allows ohmic contact with an n type impurity region formed at a silicon carbide substrate, Ni exhibits high contact resistance to a p type impurity region formed at the silicon carbide substrate. In contrast, Al allows ohmic contact with a p type impurity region formed at a silicon carbide substrate while exhibiting high contact resistance with an n type impurity region formed at the silicon carbide substrate. It was therefore extremely difficult to realize ohmic contact for both a p type impurity region and an n type impurity region formed at a silicon carbide substrate.